The Omicron family has had babies. Among the most robust: the BA.2 sub-lineage. For several weeks, it has been slowly gaining ground in France: 10.7% of interpretable sequences as of January 31, 2021, according to the latest official figures. “Preliminary data from the Flash S06 survey (07/02) confirm this increasing trend, with 14.9% of BA.2 among the 757 Omicron sequences”, indicates Public Health France in its latest report published on 17 February. After the fifth wave, should we be worried about Omicron BA. 2?
In his risk assessment on Omicron, unveiled on January 31, the Statens Serum Institute in Copenhagen indicates that BA.2 is 30% more transmissible than the BA.1 strain. If this variant appears to be more contagious than its big brother, the sublineage is unlikely to trigger a second major wave of infections, hospitalizations and deaths according to a article published on February 16 in the journal Nature. After Omicron’s assault, a large part of the population was vaccinated and/or infected with the virus, all forming a temporary health shield.
Benjamin Davido: “We won’t have a wave of BA.2s”
“I thought we were going to find ourselves in a scenario close to that of the United Kingdom or Denmark – countries where the BA.2 sub-variant has become the majority. We were one of the countries a little “in a single file” for reasons of non-sanitary restrictions too. However, in France, we do not have the impression that BA.2 is causing a rebound in contamination. Several questions arise: have we missed something on the way in which we test the population or on the tests that we use? In other words, we can wonder if the antigenic tests are lacking. Another question: have we not underestimated the true proportion of this variant On paper, BA.2 has all the scientific elements to surpass the BA1 strain, especially since its predecessor Delta left a gap to be filled.
Moreover, it is possible that the representation of BA.2 stagnates around 10 to 20%, it will perhaps be an epiphenomenon, a bit like the Delta Plus variant in India. We will not have a wave of BA.2, because the sub-variant may have difficulty continuing to establish itself in the event that the wave continues to decline. However, I can’t wait to see what happens after the February holidays – when part of the population goes skiing. We will have to see if the country experiences a resurgence of contamination. Will that be when BA.2 can catch some fresh blood? Whether in the Pyrenees or the Alps, there will be population mixing at the border. Finally, the BA.2 sub-variant is also proof that no immunity is lasting. Herd immunity will be transient and we will end up with different variants.”
Benjamin Davido, infectious disease specialist at the Raymond-Poincaré hospital in Garches (Hauts-de-Seine).
Yves Buisson: “The BA.2 sub-variant will disappear with the Omicron variant”
For the moment, it is difficult to know if the BA.2 sub-variant will become the majority in the country. Admittedly, it has been growing since its appearance, but its spread remains slow. If he was really able to spread so quickly, it would already be seen. I believe it is too close to the Omicron variant to be distinctly different in terms of circulation. Indeed, this sub-lineage does not seem to present – at least in the current state of our knowledge – notable differences with BA.1 in its contagiousness, its transmissibility and its ability to escape the immune response. To sum up, there is no need to worry: BA.2 does not seem to be more pathogenic and it is not he who should fill our hospitals and our intensive care units.
The BA.2 sub-variant can infect people who have already been vaccinated, but in my opinion without noticeable difference compared to BA.1. Among the big five variants of concern that emerged during the pandemic, some of them had sub-lineages that circulated differently in different regions of the globe. Let’s take the example of the Delta variant: in total, between 100 and 200 sub-lineages have been identified, but none of them has subsequently imposed itself, compared to the primitive Delta variant. I think we’re going to see the same thing with the Omicron variant sublineages. It is to be monitored, but they do not present any particular elements of concern. I think the BA.2 sub-variant should disappear with the Omicron variant. The latter has circulated so much that it determines a very significant collective immunity.
Yves Buisson, epidemiologist and president of the Covid-19 unit of the National Academy of Medicine.
Yves Coppieters: “What really sets him apart is his ability to transmit”
According to our current knowledge, there is nothing to worry about. If we look at the data from Denmark, we notice that the BA.2 strain is more transmissible than the BA.1. This explains why this sub-lineage could take advantage over the initial strain of the Omicron variant. The BA.2 subvariant has over a dozen different mutations, but we have not explored the effect of each of these mutations. Furthermore, we know that BA.1 possesses immune escape upon vaccination and immunity acquired through Delta. However, the hypothesis according to which BA.2 would have a stronger immune escape than BA.1 is less obvious. Once we figured out that his immune escape wasn’t entirely different from BA.1, it became reassuring.
To sum up, what really differentiates it is its transmission capacity. The BA.2 sub-variant only prolongs the Omicron wave. We are pretty sure that the sub-variant cannot be responsible for a new wave. The reason is simple: immunity seems quite effective. On the other hand, it is important to evaluate the distribution of strains in proportion to the epidemic curve. If the latter stagnates or picks up, then we will obtain a map that would allow us to make a correlation. For the moment, the increase in BA.2 – which will continue to be done – will not lead to a change in the epidemic curves.
Yves Coppieters epidemiologist at the Free University of Brussels.
Mircea Sofonea: “The BA.2 variant is likely to become the majority within two weeks”
On the current dynamic, we have reason to rejoice, because Sars-CoV-2 is circulating less and less. Let’s take a closer look: the reproduction number – the average number of new cases of a disease that a single infected and contagious person will cause on average in a population – is around 0.67. We note that it has been increasing again for five days. Be careful, this does not mean that the epidemic is picking up: just instead of having a steep decline, the latter is less rapid. Another important point: even after correcting the delay, hospitalizations (R between 0.8 and 0.85 currently) are falling less quickly than new cases. This can be explained by a drop in the screening effort.
Perhaps the epidemic is therefore circulating a little faster than what the screenings tell us. ‘Can the decline be slowed down by the spread of BA.2? It’s possible. What we see is that this sub-variant increases in frequency and there is a regional disparity. It must be understood that BA.2 is not the descendant of BA.1, but it is itself part of the Omicron group, it is a cousin. In Denmark, it spread very quickly, because it circulated almost at the same time as BA.1, while in France, it arrived much later. In France, the BA.2 variant is also likely to become the majority within two weeks.
Mircea Sofonea, epidemiologist and infectious disease modeling specialist at the University of Montpellier.
Rémi Salomon: “It is always possible to see a new wave emerge”
From what I have read, the variant is very transmissible to the point of becoming the majority in some countries. Today, everyone wants to tell themselves that the epidemic is over. We are told repeatedly that we are “at the end of the tunnel” and I think that the government is also in this perspective. Probably, it will go well until the presidential election, but we are not immune to seeing a new wave emerge. The circulation of the BA.2 sub-variant is therefore an opportunity to give a reminder of the importance of vaccination.
While the speeches are upbeat, there’s the fear that people won’t do their encores. We must not forget that if the last Omicron wave was less serious, it is because we were vaccinated. The risk is to turn the page too quickly and that we find ourselves six months later in a more problematic situation where collective immunity would be less good. I also want to remind you that the hospital is in a very bad state. He is very badly. It needs to be strengthened.
Rémi Salomon, Chairman of the Medical Commission of the Assistance Publique-Hôpitaux de Paris (AP-HP) and Chairman of the PCME Conference of French University Hospitals